The majority of semiconductor power devices are fabricated using silicon as a substrate. Recently, a trend has developed towards fabricating power devices using silicon carbide (SiC), specifically for high voltage power devices. Silicon carbide exhibits several desirable characteristics compared with silicon including the ability to operate at a high temperature, high power level, and high frequency. Additionally, silicon carbide power devices exhibit low specific on-resistance (RDSon) and high thermal conductivity, specifically 500 to 1000 times higher than silicon power devices, making it desirable for use in constructing power devices.
While silicon carbide does display these desirable characteristics, it also exhibits several non-ideal characteristics that make fabrication of trench-based power devices using silicon carbide rather difficult. The main issue associated with trench-based power device fabrication using silicon carbide is the large electric field stress imposed on the oxide lining the trench during device operation. Because the critical field for breakdown in silicon carbide is so high, it causes a large field to exist in the oxide lining the trench during operation. This high electric field stress will lead to catastrophic breakdown of the oxide. Several techniques exist for reducing this field stress, but these techniques either degrade the on-resistance of the device, or are impractical to implement during fabrication.
It is within this context that embodiments of the present invention arise.